I have 3 computers in my home: mine, my wife’s, and my work computer. Both my wife and I run Windows 7 with the latest Avast. My work computer is running Windows 7 with Symantec AV. Almost as soon as I turn on my wife’s computer, Symantec on my work computer pops up a message saying it blocked a port scan attack from her IP address. I have run the full AV scan on my wife’s computer but it didn’t find any virus. What else would cause her computer to run a port scan?
guessing it is some windows activity that a nervous Norton firewall detect…
but to be 100% sure, follow the sticky guide in virus and worms section and attach the requested logs
http://forum.avast.com/index.php?topic=53253.0
AdwCleaner
Malwarebytes
OTL
aswMBR
then a malware specialist will be notified and check the logs for infections
Are you networked (i.e. file sharing with the other computer)